Debian

Debian is an OS that uses the Linux kernel. Although it is usually set up on personal computers, it's being used on more and more web servers as well. The reason is that it is very stable, so a server running it will not have to be restarted for months. Debian is also considered to be among the most risk-free Operating Systems available, due to the fact that security patches are released within days after an issue is discovered. This is possible since thousands of experienced developers are employed by the Debian project on a voluntary basis and not only do they work on the OS itself, but they also provide 24/7 support via special mailing lists and reply in 20 min to any question. Thus, you will have top-level support directly from the developers who know their own platform in depth, and not from a third-party support team. Debian is also one of the Linux releases with the highest number of packages - more than 30,000. Since the Operating System is completely free to use, you are able to modify both the core and all the packages in the way you see fit. In addition, you will not have to pay any kind of license fees.